Rigid crankshaft cradle and actuator

ABSTRACT

Crankshaft main bearing failure in variable compression ratio engines having eccentric main bearing supports is prevented by supporting the bearings in a crankshaft cradle ( 16 ) having a high stiffness and a high natural frequency. The crankshaft cradle ( 16 ) is rotatable mounted in the engine on a first axis, and the crankshaft ( 8 ) is mounted in the crankshaft cradle ( 16 ) on a second axis off-set from the first axis, the first axis and the second axis defining a first plane. The crankshaft cradle comprises a primary eccentric member ( 24 ) and a plurality of smaller bearing caps ( 26 ) separated by a parting line. The crankshaft cradle comprises accentric members ( 24 ) that support the bearing element ( 64 ), and structural webbing ( 72 ) that rigidly holds the eccentric members ( 24 ) in alignment with one another at all times.

PROVISIONAL APPLICATION REFERENCE

This application relates to U.S. Provisional Application No. 60/164,774,having a filing date of Nov. 12, 1999.

BACKGROUND OF THE INVENTION

The present invention relates to a method and apparatus for adjustingthe compression ratio of internal combustion engines, and morespecifically to a method and apparatus for adjusting the position of thecrankshaft with eccentric crankshaft main bearing supports.

Designs for engines having eccentric crankshaft main bearing supportshave been known for some time. In these engines the eccentric mainbearings are rotated to adjust the axis of rotation of the crankshaft.Significant forces bear down on the eccentric main bearing supportsduring operation of the engine, causing the eccentric main bearingsupports to twist out of alignment. Poor alignment of the eccentric mainbearing supports is a problem for these engines because even smallamounts of main bearing misalignment can cause rapid main bearingfailure. Another problem with engines having eccentric main bearingsupports is that of a low natural frequency of vibration. Operation ofthese engines at or near the natural frequency of the eccentric mainbearing supports can destroy the engine. The low natural frequency ofthese engines is a problem because the engines cannot be operated atspeeds necessary for use of the engine in passenger cars, trucks, andother applications.

Engines having only one cylinder and two main bearings can tolerate muchgreater twisting of the main bearing supports, because the crankshaft isfree to self align within the two bearings. Single cylinder engines,however, are not employed in the major automobile markets. An objectiveof the present invention is to provide an eccentric main bearing supportfor engines having more than one cylinder that provides a long mainbearing life, a high natural frequency, and a low manufacturing cost.Another objective of the present invention is to provide an eccentricmain bearing support that does not significantly alter overall enginesize and mass. Further objectives of the present invention are toprovide a compact eccentric main bearing support that permits balancingof primary cranktrain forces and use of a conventional connecting rodhaving a length no more than two and one quarter times the stroke of theengine.

European patent EP 345-366-A issued to Buffoli Dec. 13, 1989 shows avariable compression ratio engine having a lower main bearing support 30and an upper main bearing support 41 fastened together with screws 49.The force applied to the main bearing supports causing them to twist isproportional to the cross sectional area of the power cylinder bore andthe power cylinder pressure. Main bearing support 30 includes five lowerhemispherical disc segments joined by lower webbing. FIG. 1 of EP345-366-A shows the webbing to have a small cross sectional arearelative to the cross sectional area of the power cylinder bore. FIG. 1also shows that the cross sectional area of the lower webbing is about3.8% of the projected area of the eccentric member assembly, where thearea of the eccentric member is projected on a plane perpendicular tothe axis of rotation of the crankshaft. The lower webbing also has ashort length, and spans a small arcuate length about the pivot axis ofthe main bearing support, about 63 degrees. The webbing with its smallarea and short length fails to provide rigid support of the mainbearings. Furthermore, the part has a low natural frequency due to itslack of rigidity. The length and area of the webbing can only beextended downward a small amount without causing mechanical interferencewith the connecting rod.

Similarly, main bearing support 41 includes five upper hemisphericaldisc segments joined by upper webbing. FIG. 1 also shows the upperwebbing to have a small cross sectional area relative to the size of thecross sectional area of the power cylinder bore. The upper webbing has ashort length, and spans a small arcuate length about the pivot axis ofthe main bearing support. The length and area of the upper webbingcannot be significantly increased upward without causing mechanicalinterference with the connecting rod. The small cross sectional area ofthe upper and lower webbing and the small arcuate length of the upperand lower webbing is incapable of maintaining precise alignment of themain bearings, and consequently the main bearings of the engine shown inEP 345-366-A would fail. Furthermore, the main bearing supports have anatural frequency too low for the engine to be commercially viable. Thenatural frequency is exceptionally low because the webbing shown doesnot provide a rigid structure and the eccentric discs are massiverelative to the size of the webbing. Additionally, because the upper andlower bearing main supports are tightly fastened together with screws,the mass of the upper bearing support is likely to even further lowerthe natural frequency of the lower main bearing support, and the mass ofthe lower bearing support is likely to even further lower the naturalfrequency of the upper bearing support. The outer diameter of the mainbearing supports could be increased and the webbing made thicker toincrease rigidity, however, the increased mass of the disc segmentswould adversely effect the natural frequency of the main bearingsegments.

Accordingly, and objective of the present invention is to provide, inmulti-cylinder engines having eccentricly supported crankshaft mainbearings, rigid support and rigid alignment of the crankshaft mainbearings at all times to provide a long main bearing life. A furtherobjective of the present invention is to provide a high naturalfrequency for the eccentric supports to permit operation of the engineover the range of speeds required for commercial use of the engine.

SUMMARY OF THE INVENTION

In the present invention, a crankshaft cradle, made up of a largeprimary eccentric member and small main bearing caps, is employed torigidly hold the crankshaft main bearings in alignment. The parting linebetween the primary eccentric member and the main bearing caps isoriented approximately vertically, or approximately parallel with thepower cylinder line of action. Additionally, the bearing cap fastenersare located horizontally above (closer to the piston) and below thecrankshaft, and the bearing cap bridge thickness minimized in order tolocate the crankshaft main bearings in close proximity to the crankshaftcradle outer diameter. According to the present invention, the primaryeccentric member is made up of eccentric disc segments rigidly joined bywebbing, the arcuate span of the webbing about the eccentric discsegments being greater than 120 degrees, and preferably greater than 150degrees. The large arcuate span of the webbing is made possible by thelarge size of the primary eccentric member relative to the main bearingcaps, by the vertical orientation of the parting line, and by placementof the crankshaft main bearings in close proximity to the crankshaftcradle outer diameter. According to the preferred embodiment of thepresent invention, the cross sectional area of the webbing within the120 degree arcuate span is greater than 35 percent of the crosssectional area of the cradle within the same 120 degree arcuate span.Concurrently the diameter of the primary eccentric member is preferablyless than 2.5 times the diameter of the power cylinder and less than 4times the working diameter of the crankshaft main bearing to provide ahigh natural frequency. Preferably, at mid span between the eccentricdiscs the cross sectional area of the webbing is greater than 40 percentof the cross sectional area of the power cylinder. The large contiguousarea of the webbing provides a high rigidity and a high stiffness forthe primary eccentric member, and precise alignment of the main bearingsat all times, which in turn provides a long bearing life, and the smalldiameter of the eccentric discs provides a light weight and a highnatural frequency, permitting operation of the engine over the fullspeed range required for commercial use of the engine.

The webbing is deeply scalloped towards the eccentric discs to providefurther support, to further minimize twisting of the primary eccentricmember under firing engine loads and to further increase the naturalfrequency of the crankshaft cradle. Preferably at one forth span betweenthe eccentric disc segments the cross sectional area of the webbing isat least 20 percent greater than the cross sectional area of the webbingat mid span between the eccentric discs. Preferably the primaryeccentric member is a single cast piece, and the webbing is contiguousand has no large holes. Additionally, in the preferred embodiment of thepresent invention the overall mass of the bearing caps is less than 25percent of the mass of the primary eccentric member, and consequentlythe bearing caps cause only a small reduction in natural frequency.According to the preferred embodiment of the present invention, thecrankshaft cradle has a natural frequency greater than 100 Hz.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows a sectional elevation view of the variable compressionratio mechanism according to the present invention taken along cut linesB—B shown in FIG. 2.

FIG. 2 shows a bottom view of the variable compression ratio engineaccording to the present invention along cut lines A—A shown in FIG. 1,with the connecting rod and pistons removed to show the crankshaft.

FIG. 3 shows a top view of a portion of the crankshaft cradle shown inFIGS. 1 and 2.

FIG. 4 shows the cross sectional webbing area of the crankshaft cradleshown in FIGS. 1, 2 and 3.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a portion of a variable compression ratio mechanism 1 in avariable compression ratio engine 2 according to the present invention.Engine 2 has a piston 4, a connecting rod 6, a crankshaft 8 having anaxis of rotation 10, a power cylinder 12 having a cross sectional area13 in an engine block 14, a crankshaft cradle 16 having a pivot axis 18,an optional power take-off shaft or balance shaft 20, and an optionalbedplate or cradle bearing cap 22. Connecting rod 6 connects piston 4 tocrankshaft 8 for reciprocating motion of piston 4 in cylinder 12. Cradle16 includes a primary eccentric member 24 and a plurality of mainbearing caps 26 and a plurality of fasteners 28 for removably fasteningbearing caps 26 to primary eccentric member 24 for rotatably supportingcrankshaft 8 in crankshaft cradle 16. Engine 2 further includes acontrol shaft 30 mounted in engine block 14 having one or more off-setjournals 32, one or more one or more control pins 34 mounted in cradle16 and one or more control arms 36 connecting control shaft 30 andcontrol pin 34, control arm 36 being rotatably mounted on off-setjournal 32. Rotation of control shaft 30 pivots off-set journal 32causing control arm 36 to move causing cradle 16 to pivot about pivotaxis 18 causing crankshaft axis of rotation 10 to move causing thecompression ratio of engine 2 to change.

FIG. 2 shows a bottom view of engine 2 according to the presentinvention along cut lines A—A shown in FIG. 1, with pistons 4 andconnecting rods 6 removed to show crankshaft 8. In the embodiment shown,crankshaft 8 and balance shaft 20 include gears 38. In the preferredembodiment of the present invention gears 38 transfer power fromcrankshaft 8 to power take-off shaft 20, and power take-off shaft 20transfers power out of engine 2. Gears 38 may have helical teeth orstraight cut teeth, and gears 38 may include a single helical gear pairor a double helical gear pair (shown) for neutralizing axial thrustloads caused by the helix angle of the gear teeth. Power take-off shaft20 may include balance webs 40 for balancing primary (shown) orsecondary engine forces. Crankshaft 8 includes crank balance webs 42.

Crankshaft 8 is preferably mounted in journal main bearings 44. Oil isfed to journal bearings 44 through an oil galley 46 and oil feeds 48located in cradle 16. Preferably, oil is fed to oil galley 46 in cradle16 through oil fitting 50, oil fitting 50 preferably being located onpivot axis 18. Oil fitting 50 includes an oil feed line 52 in fluidcommunication with oil galley 46, oil feeds 48 and journal bearings 44.Preferably oil feeds 48 are located between fasteners 28 to provide arigid mid section of primary eccentric member 24.

Crankshaft 8 may include a first flywheel 54, and power take-off shaft20 may include a second flywheel 56 having a rotational directionopposite that of the first flywheel 54 to provide reduced enginevibration according to the principles disclosed in U.S. Pat. No.3,402,707 issued to Paul Heron on Sep. 24, 1968. In the preferredembodiment of the present invention, power take-off shaft 20 includes afirst end 58 located in close proximity to gears 38, and a second end60, where power take-off from the engine 2 is through first end 58 ofpower take-off shaft 20, thereby providing low torsional loads throughthe length of power take-off shaft 20, and a larger direct force and asmaller alternating force on gears 38. Second flywheel 56 is located onthe first end 58 of power take-off shaft 20, and first flywheel 54 islocated on the far end of crankshaft 8. Flywheel 56 may span acrosscrankshaft rotational axis 10 (shown), and flywheel 54 may span acrossthe rotational axis of power take-off shaft 20 (shown) to provide aminimum spacing between crankshaft 8 and power take-off shaft 20, inorder to provide optimum engine balancing and a small engine size. Avalve gear sprocket or chain 62 (shown), belt, gear or other type ofdrive is preferably located on the second end 60 of power take-off shaft20 for driving the valvetrain and/or other engine accessories, it beingunderstood that more than one drive may be located on power take-offshaft 20. Preferably chain 62 is located adjacent to flywheel 54, andbetween flywheel 54 and flywheel 56, to provide a compact engine size.

Referring now to all of the figures, according to the preferredembodiment of the present invention engine 2 has a variable compressionratio mechanism 1, a plurality of cylinders 12, it being understood thatengine 2 may alternatively have only one cylinder, a piston 4 mountedfor reciprocating movement in each of cylinders 12, crankshaft 8 has anaxis of rotation 10, and connecting rod 6 connects each piston 4 tocrankshaft 8. Referring now to FIGS. 1, 2, and 3, connecting rod 6 has aconnecting rod crankshaft bearing 64 having a mid span 66, mid span 66being shown in FIGS. 2 and 3. Cradle 16 supports crankshaft 8 forrotation of crankshaft 8 about axis of rotation 10, and cradle 16 ismounted in engine 2 for pivoting relative to engine 2 about pivot axis18, pivot axis 18 being substantially parallel to and spaced fromcrankshaft rotational axis 10. An actuator 68 (shown in FIG. 2) ismounted on one end of control shaft 30 for varying the position ofcradle 16 about pivot axis 18 for varying the position of crankshaftaxis of rotation 10, it being understood that a rotary actuator (shown),a hydraulic cylinder type actuator, or another functional type ofactuator may be employed to adjust the rotational position of cradle 16about pivot axis 18. Cradle 16 includes primary eccentric member 24 anda plurality of bearing caps 26 and a plurality of bearing cap fasteners28 for removably fastening each bearing cap 26 to primary eccentricmember 24. According to the present invention, primary eccentric member24 comprises a plurality of disc segments 70 and webbing 72, discsegments 70 being rigidly jointed together by webbing 72. Preferably,primary eccentric member 24 comprising eccentric discs 70 and webbing 72is a single cast piece. Crankshaft axis of rotation 10 and pivot axis 18define a first plane 74, and each bearing cap 26 has a primary contactsurface 76 for contact with primary eccentric member 24, primary contactsurface 76 being within ±30 degrees of perpendicular to first plane 74,and fasteners 28 are within ±30 degrees of parallel to first plane 74for providing space on the far side of the cradle from bearing caps 26for a large and contiguous webbing 72. Primary contact surface 76 isgenerally perpendicular to the clamping force line of action offasteners 28, and may be a single flat surface (shown), a serrated orfractured surface where the surface texture of the serration or fractureprovides alignment and prevents slip between the bearing caps 26 andprimary eccentric member 24, and in such cases primary contact surface76 may be approximated as a generally flat surface where the minorsurface irregularities are ignored. Dowels, stepped joints, fittedbolts, and other functional means may be employed to prevent slipbetween primary eccentric member 24 and bearing caps 26 such asconfigurations shown in Bearings, a Tribology Handbook, Edited by M. J.Neale, Reed Educational and Professional Publishing Ltd., 1998, page 61.Crankshaft 8 is mounted in main bearings 44, main bearings 44 have aworking diameter 78 (shown in FIG. 4) and a main bearing mid span 80(shown in FIGS. 2 and 3), and bearing caps 26 have a bridge thickness82, the bridge thickness 82 of at least one bearing cap being less than70 percent of the thickness of at least one crankshaft bearing workingdiameter 78, and preferably less than half the thickness of at least onecrankshaft bearing working diameter 78, for location of crankshaft 8adjacent to the outer diameter of the cradle for providing space for alarge web on the far side of the cradle from the bearing caps. Mainbearing mid span 80 is located at the center of the radial load bearingportion of the bearing along the axial length of the bearing. Bridgethickness 82 is measured with main bearing 44 removed, and is theshortest distance measured on first plane 74 across bearing cap 26. Forengines with a variable bridge thickness as measured at various axiallocations of main bearing 44, bridge thickness 82 is the average bridgethickness being in radial load bearing contact with main bearing 44.

Each bearing cap 26 has an upper contact face length or upper centeringdistance 75 and a lower contact face length or lower centering distance77 (shown in FIG. 4), each centering distance spanning from main bearing44 to cradle bearings 122 along the plane of primary contact surface 76.Pivot axis 18 and bearing working diameter (e.g., the crankshaft bearingsurface) 78 may be separated by a fitting distance 79 to provide accessfor oil feed line 52. Preferably, the lower centering distance 77 is atleast 1.5 times longer than fitting distance 79. Preferably lowercentering distance 77 is at least twice as long as bridge thickness 82to position the crankshaft near the outer diameter of the crankshaftcradle.

Webbing 72 has a first thick section 84 (shown in FIG. 4) located withina 120 degree arcuate span 88 about pivot axis 18 and located on a secondplane 85 perpendicular to pivot axis 18, perpendicular to first plane 74and passing through the mid span 66 of connecting rod crankshaft bearing64, first thick section 84 having an outer perimeter 86. First thicksection 84 is preferably a single cast piece. The arcuate span ofwebbing 72 being greater than 120 degrees about the pivot axis in thepreferred embodiment of the present invention, and preferably greaterthan 150 degrees. 120 degree arcuate span 88 has an arcuate area 90located within outer perimeter 86 and within 120 degree arcuate span 88.First thick section 84 has a first thick section cross sectional area92, the cross sectional area of first thick section 92 being greaterthan 25 percent of arcuate area 90, and preferably greater than 35percent of arcuate area 90, in order to provide crankshaft cradle 16with a high stiffness and a high natural frequency of vibration. Forengines according to the present invention having webbing 72 that spansmore than 120 degrees about pivot axis 18, 120 degree arcuate span 88falls within the arcuate span of webbing 72. For engines according tothe present invention having webbing 72 that spans less than 120 degreesabout pivot axis 18, 120 degree arcuate span 88 is centered aboutwebbing 72. Preferably webbing 72 has an arcuate span about pivot axis18 of at least 120 degrees on second plane 85 and perpendicular to firstplane 74, for providing a rigid cradle having a high natural frequency.

Preferably, primary eccentric member 24 has a first overall mass, andthe removable bearing caps 26 have a second overall mass, the secondoverall mass being less than 25 percent of the first overall mass, inorder to provide a high natural frequency. According to the preferredembodiment of the present invention, cradle 16 has a natural frequencygreater than 100 hertz, however, cradle 16 may have a lower naturalfrequency in some embodiments of the present invention.

Referring to FIGS. 1 and 4, webbing 72 may include one or more holes 94for reducing the weight of cradle 16 or for draining engine oil awayfrom the spinning crankshaft or for another purpose. Preferably webbing72 has no single hole 94 spanning more than 60 degrees within said 120degree arcuate span 88. Webbing 72 further comprises holes 95 in primaryeccentric member 24 for fasteners 28, where between adjacent discssegments 70 webbing 72 is located on both sides of each hole 95 forproviding additional structure (e.g., webbing is located above and beloweach hole 95 as shown in FIG. 1). Preferably main bearing cap 26includes tapped holes 97 for retaining fasteners 28, and fasteners 28are screws having an accessible head in primary eccentric member 24 forassembly, in order to provide a bearing cap having a maximum thicknessand a maximum strength and stiffness. Alternatively, fasteners 28 may bebolts having an approximately oval head 99, oval heads 99 being seatedin main bearing cap 26.

Referring now to FIGS. 2, 3, and 4, webbing 72 includes scalloping 96between eccentric discs 70 for increasing the rigidity and the naturalfrequency of primary eccentric member 24. FIG. 2 shows a sectional viewof scalloping 96 on first plane 74. The profile of scalloping 96 isindicated by a dashed line in FIG. 3. FIG. 3 shows a top view of aportion of the cradle 16 shown in FIG. 2, and FIG. 2 shows a bottomsectional view of cradle 16. Referring to FIG. 3, line 98 is intended toindicate the profile of scalloping at the top of eccentric member 24closest to piston 4. Scalloping profile 98 is indicated by a dashed linein FIG. 4. Similarly, line 100 in FIG. 3 is intended to indicate theprofile of scalloping at the bottom of eccentric member 24. Scallopingprofile 100 is indicated by a dashed line in FIG. 4. Referring now toFIGS. 3 and 4, due to scalloping, the sectional area of webbing 72 isgreater near eccentric discs 70, and smaller towards mid span 66.According to the present invention, scalloping increases the rigidityand increases the natural frequency of primary eccentric member 24 andcradle 16. As previously described, webbing 72 has a first thick section84 having a first thick section cross sectional area 92 located on asecond plane 85. Primary eccentric member 24 has a second thick section102 having a second thick section cross sectional area 104 located on athird plane 106 located parallel to second plane 85, perpendicular topivot axis 18 and perpendicular to first plane 74 and located withinarcuate span 88. Second plane 85 and main bearing mid span 80 beingseparated by a first distance 108, second plane 85 and third plain 106being separated by a second distance 110, second distance 110 being halfas long as first distance 108. Preferably, according to the presentinvention, second thick section cross sectional area 104 is at least 10percent greater than first thick section cross sectional area 92 forproviding a rigid cradle 16 and a high natural frequency.

Primary eccentric member 24 has a third thick section 112 having a thirdthick section cross sectional area 114 located on a forth plane 116located parallel to second plane 85, perpendicular to pivot axis 18 andperpendicular to first plane 74, and located within arcuate span 88.Second plane 85 and forth plane 116 being separated by a third distance120, third distance 120 being 60 percent as long as long as firstdistance 108. Preferably, according to the present invention, thirdthick section cross sectional area 114 is at least 15 percent greaterthan first thick section cross sectional area 92 for providing a rigidcradle 16 and a high natural frequency.

Referring now to FIG. 1, preferably each bearing cap 26 is fastened toprimary eccentric member 24 by at least two first fasteners 28, thefirst fastener and the second fastener being located approximatelyperpendicular to primary contact surface 76, and the first fastener islocated on the far side of crankshaft main bearing 44 from the secondfastener.

Referring now to FIG. 4, cradle 16 is supported by one or more cradlebearings 122 having a cradle bearing diameter 124 for pivotallysupporting cradle 16 about pivot axis 18. Cradle bearing diameter 124 ispreferably no more than 4 times crankshaft bearing working diameter 78in order to provide a cradle having a low mass, a low polar moment ofinertia, and a high natural frequency. Cradle 16 may have cradlebearings diameters 124 of various diameters, and may have crankshaftbearing working diameters 78 of various diameters, in some embodimentsof the present inventions. Cradle bearing diameter 124 is the averagebearing diameter of the bearings supporting cradle 16, and crankshaftbearing working diameter 78 is the average bearing diameter of thebearings supporting crankshaft 8 in embodiments having dissimilarbearing diameters, where average diameter is determined by weighting thebearings for their axial length (e.g., the sum of each bearing diametertimes its load bearing axial length in the numerator, and the sum of theaxial load bearing lengths of the bearings in the denominator).Optimally bridge thickness 82 is no more than half the thickness of atleast one crankshaft bearing working diameter 78 in order to provide acradle having a low mass, a low polar moment of inertia, and a highnatural frequency.

Accordingly, the present invention provides, in multi-cylinder engineshaving eccentricly supported crankshaft main bearings, rigid support andrigid alignment of the crankshaft main bearings at all times for providea long main bearing life. The present invention provides a high naturalfrequency for the eccentric supports permitting operation of the engineover the range of speeds required for commercial use of the engine.Additionally, the present invention can be manufactured at a low cost.Those skilled in the art will recognize that the invention can bepracticed with modifications within the spirit and scope of the claims.For example, the present invention may be employed in compressors,pumps, and expanders, and also in single cylinder as well asmulti-cylinder machines.

What is claimed is:
 1. A variable compression ratio mechanism for areciprocating piston machine having one or more cylinders, a pistonmounted for reciprocating movement in each of said cylinders, acrankshaft defining an axis about which the crankshaft rotates, and aconnecting rod connecting each of said pistons to the crankshaft, saidconnecting rod having a connecting rod crankshaft bearing having a midspan, comprising; a crankshaft cradle supporting the crankshaft forrotation of the crankshaft about the rotational axis of the crankshaft,said cradle having an outer cradle bearing diameter for pivotallysupporting said cradle in the reciprocating piston machine about a pivotaxis, said pivot axis being concentric with said outer cradle bearingdiameter, the pivot axis being substantially parallel to and spaced fromthe rotational axis of the crankshaft, wherein said cradle is mounted insaid reciprocating piston machine and motion of said outer cradlebearing diameter is restricted by said reciprocating piston machine topivoting about said pivot axis, thereby substantially preventingreciprocating motion of said cradle in said reciprocating machine, anactuator for varying the position of the cradle about the pivot axis forvarying the position of the rotational axis of the crankshaft, saidcradle comprising a primary eccentric member, a plurality of bearingcaps, and a plurality of bearing cap fasteners for removably fasteningeach bearing cap to the primary eccentric member, wherein said primaryeccentric member comprises a plurality of disc segments and webbing,said disc segments being rigidly joined together by said webbing,wherein a portion of said webbing and at least two of said disc segmentsare a single cast piece, said crankshaft axis and said pivot axisdefining a first plane, said bearing caps having a primary contactsurface for contact with said primary eccentric member, a portion ofsaid primary contact surface being within 40 degrees of perpendicular tosaid first plane, and at least one of said fasteners being within 40degrees of parallel to said first plane for providing space on the farside of the cradle for a large and contiguous webbing, said crankshafthaving a plurality of main bearings, said main bearings having a workingdiameter and a main bearing mid span, and said bearing caps having abridge thickness, said bridge thickness being the distance on said firstplane between said outer cradle bearing diameter and said crankshaftmain bearing, the bridge thickness of at least one bearing cap beingless than 70 percent of the thickness of at least one crankshaft mainbearing working diameter, for location of the crankshaft adjacent to theouter diameter of the cradle for providing space for a large web on thefar side of the cradle, said reciprocating piston machine having asecond plane perpendicular to said pivot axis and perpendicular to saidfirst plane and passing through said connecting rod crankshaft bearingmid span, wherein said cradle has webbing between at least two adjacenteccentric discs, said webbing being located on said second plane over anarc distance about said pivot axis greater than 120 degrees, therebyproviding a crankshaft cradle with a high stiffness.
 2. The variablecompression ratio mechanism of claim 1, wherein the reciprocating pistonmachine is an engine.
 3. The variable compression ratio mechanism ofclaim 1, wherein the reciprocating piston machine is has two or morecylinders.
 4. The variable compression ratio mechanism of claim 1,wherein said webbing has a first thick section located within a 120degree arcuate span about said pivot axis and located on said secondplane, said first thick section having an outer perimeter, said 120degree arcuate span having an arcuate area located within said outerperimeter and within said 120 degree arcuate span, said first thicksection having a first cross sectional area, said first cross sectionalarea of said first thick section being greater than 25 percent of saidarcuate area, thereby providing a rigid cradle having a high naturalfrequency.
 5. The variable compression ratio mechanism of claim 1,wherein the primary eccentric member has a first overall mass, and theremovable bearing caps have a second overall mass, the second overallmass being less than 25 percent of the first overall mass, therebyproviding a crankshaft cradle with a high natural frequency.
 6. Thevariable compression ratio mechanism of claim 1, wherein the webbing hasno single hole spanning more than 60 degrees within said 120 degrees onsaid second plane.
 7. The variable compression ratio mechanism of claim1, wherein the cradle has a natural frequency greater than 100 hertz. 8.The variable compression ratio mechanism of claim 1, wherein the webbingincludes scalloping between at least two adjacent disc segments forincreasing the rigidity and the natural frequency of the primaryeccentric member.
 9. The variable compression ratio mechanism of claim8, wherein the webbing between said two adjacent disc segments has asecond thick section having a second thick section cross sectional arealocated on a third plane parallel to said second plane and perpendicularto said pivot axis, said second thick section cross sectional area beinglocated within said 120 degrees about said pivot axis, said second planeand said main bearing mid span being separated by a first distance, saidsecond plane and said third plane being separated by a second distance,said second distance being 60 percent as long as said first distance,wherein said second thick section cross sectional area is at least 15percent greater than said first thick section cross sectional area. 10.The variable compression ratio mechanism of claim 1, wherein eachbearing cap is fastened to said primary eccentric member by at least afirst fastener and a second fastener, said first fastener and saidsecond fastener being located approximately perpendicular to saidportion of said primary contact surface, and said first fastener beinglocated on the far side of said crankshaft main bearing from said secondfastener.
 11. The variable compression ratio mechanism of claim 1,further comprising cradle bearings for pivotally supporting said cradleabout said pivot axis, said cradle bearings having a cradle bearingdiameter, said cradle bearing diameter being no more than 4 times saidworking diameter, thereby providing a cradle having a low mass, a lowpolar moment of inertia, and a high natural frequency.
 12. The variablecompression ratio mechanism of claim 1, wherein said bridge thickness isno more than half the thickness of at least one crankshaft bearingworking diameter, thereby providing a cradle having a low mass, a lowpolar moment of inertia, and a high natural frequency.
 13. The variablecompression ratio mechanism of claim 1, wherein said portion of saidprimary contact surface is within ±30 degrees of perpendicular to saidfirst plane.
 14. The variable compression ratio mechanism of claim 1,wherein the webbing includes holes within said 120 degrees on saidsecond plane.
 15. The variable compression ratio mechanism of claim 1,further comprising holes in said primary eccentric member for saidfasteners, wherein between adjacent disc segments said webbing islocated on both sides of each of said holes for providing additionalstructure.
 16. The variable compression ratio mechanism of claim 1,further comprising tapped holes in said bearing cap, wherein saidfasteners are screws having an exposed head in said primary eccentricmember for providing a maximum thickness bearing cap having a maximumstrength and stiffness.
 17. The variable compression ratio mechanism ofclaim 1, wherein said fasteners are bolts having an oval head, said ovalheads being seated in said bearing cap.
 18. The variable compressionratio mechanism of claim 4, wherein said first cross sectional area ofsaid first thick section is greater than 35 percent of said arcuatearea, thereby providing a crankshaft cradle with a high stiffness and ahigh natural frequency of vibration.
 19. The variable compression ratiomechanism of claim 1, wherein at least one of said bearing caps has alower centering distance spanning from said working diameter to theouter diameter of said cradle along the plane of said portion of saidprimary contact surface, said pivot axis and said working diameter beingseparated by a fitting distance, wherein said lower centering distanceis at least 1.5 times as long as said fitting distance for providingspace on the far side of the cradle for a large webbing.
 20. Thevariable compression ratio mechanism of claim 1, wherein at least one ofsaid bearing caps has a lower centering distance spanning from saidworking diameter to the outer diameter of said cradle along the plane ofsaid portion of said primary contact surface, wherein said lowercentering distance is at least twice as long as said bridge thicknessfor providing space on the far side of the cradle for a large webbing.21. The variable compression ratio mechanism of claim 1, furtherincluding a power take off shaft having a first pair of helical gears,said power take off shaft being mounted in said variable compressionratio machine, and said crankshaft having a second pair of helical gearsin mesh with said first pair of helical gears for transferring powerfrom said crankshaft to said power take off shaft, said first pair ofhelical gears having helix angles for neutralizing axial thrust loads onthe cradle caused by the helix angle of the gear teeth.
 22. A variablecompression ratio mechanism for a reciprocating piston machine havingone or more cylinders, a piston mounted for reciprocating movement ineach of said cylinders, a crankshaft defining an axis about which thecrankshaft rotates, and a connecting rod connecting each of said pistonsto the crankshaft including; a crankshaft cradle supporting thecrankshaft for rotation of the crankshaft about the rotational axis ofthe crankshaft, said cradle having an outer cradle bearing diameter forpivotally supporting said cradle in the reciprocating piston machineabout a pivot axis, said pivot axis being concentric with said outercradle bearing diameter, the pivot axis being substantially parallel toand spaced from the rotational axis of the crankshaft, wherein saidcradle is mounted in said reciprocating piston machine and motion ofsaid outer cradle bearing diameter is restricted by said reciprocatingpiston machine to pivoting about said pivot axis, thereby substantiallypreventing reciprocating motion of said cradle in said reciprocatingmachine, a cradle pin mounted in said cradle, and an eccentric pinmounted in said reciprocating machine, a link connecting said cradle pinand said eccentric pin, and an actuator for rotating said eccentric pin,wherein rotating said eccentric pin adjusts the position of said linkand adjusts the rotational position of the cradle, and adjusts theposition of the crankshaft rotational axis, and adjusts the compressionratio of said reciprocating piston machine.
 23. The variable compressionratio mechanism of claim 22, wherein said cradle comprises a primaryeccentric member, a plurality of bearing caps, and a plurality ofbearing cap fasteners for removably fastening each bearing cap to theprimary eccentric member, wherein said primary eccentric membercomprises a plurality of disc segments and webbing, said disc segmentsbeing rigidly joined together by said webbing, and a first and a secondfastener passing through at least one of said disc segments forfastening said bearing cap to said disc segment, said first fastenerdefining a first fastener axis concentric with the shaft of said firstfastener, and a second fastener defining a second fastener axisconcentric with the shaft of said second fastener, and said cradle pinhas a cradle pin axis being concentric with the outer diameter of saidcradle pin, wherein said cradle pin axis passes between said firstfastener axis and said second fastener axis, for providing a rigidcradle structure.